The progressive improvement of electronic systems, such as microcontroller and microprocessor based applications for the control of motors, as well as the availability of improved portable power sources, has made the development of efficient electric motor drives for vehicles, as a viable alternative to internal combustion engines, a compelling challenge. Electronically controlled pulsed energization of windings of motors offers the prospect of more flexible management of motor characteristics. By control of pulse width, duty cycle, and switched application of a battery source to appropriate stator windings, functional versatility that is virtually indistinguishable from alternating current synchronous motor operation can be achieved. The use of permanent magnets in conjunction with such windings is advantageous in limiting current consumption.
The above-identified copending related U.S. patent application Ser. No. 09/826,422 of Maslov et al. identifies and addresses the need for an improved motor amenable to simplified manufacture and capable of efficient flexible operating characteristics. In a vehicle drive environment, it is highly desirable to attain smooth operation over a wide speed range, while maintaining a high torque output capability at minimum power consumption. Such a vehicle motor drive should advantageously provide ready accessibility to the various structural components for replacement of parts at a minimum of inconvenience. The copending related U.S. application incorporates electromagnet poles as isolated magnetically permeable structures configured in an annular ring, relatively thin in the radial direction, to provide advantageous effects. With this arrangement, flux can be concentrated, with virtually no loss or deleterious transformer interference effects in the electromagnet cores, as compared with prior art embodiments. While improvements in torque characteristics and efficiency are attainable with the structure of the identified copending application, further improvements remain desirable.
To this end, the above-identified copending related U.S. patent application Ser. No. 09/826,423 of Maslov et al. seeks to optimize rotor parameters such as the grade of the magnet, the energy density and the overall magnetic characteristics of the magnet grade, the size and the dimensions of the magnet that can adjust the permanence and the overall operating condition of the magnet when it is part of the rotor, the temperature stability of the magnet, the finishing, coating and post processing steps taken in manufacturing of the magnets for the intended application, the stability of the magnetization over the curvilinear surface of the magnet, uniformity of the radial polarization of the magnet, the adjacent gap between two separate magnets, the mechanical features of the edges of the magnets, and the return flux path of the magnet as provided by a back iron ring section.
In environments in which portability and size are important factors, the need exists for drive motors that are capable of a wide range of operating characteristics, without sacrificing complex control functionality. Brushless motor systems should have the capability to control each of a plurality of electronic switches to provide accurate commutation sequencing and appropriate application of power to the individual stator windings. The above-identified copending related U.S. patent application Ser. No. 09/966,102 of Maslov et al. describes a motor structural configuration in which the control elements, which can be complex and diverse, are contained within the confines of the stator. The stator flux producing structure, streamlined to a relatively thin annular configuration to accommodate placement of the elements therein, nevertheless is capable of producing appropriate flux output while providing high torque at low operating speeds.
Various advantages attributable to the provision of multiple separate stator magnetic paths in comparison to a single common path in the stator body have been described above. Easy accessibility to the interior of the stator and the structural and electrical components therein present additional opportunities for improved operation.